Lead zirconate titanate (PZT: Pb(ZrxTi1-x)O3, 0<x<1) is a typical ferroelectric material capable of storing a large amount of electric charge, and used in capacitors and film memories. PZT has pyroelectricity and piezoelectricity based on the ferroelectricity thereof. PZT has high piezoelectric performance, and its mechanical quality factor Qm can be controlled easily by adjusting the composition or adding an element thereto. This allows PZT to be applied to sensors, actuators, ultrasonic motors, filter circuits, and oscillators.
PZT, however, contains a large amount of lead. In recent years, there has been a growing concern that lead leached from waste may cause serious damage to the ecosystem and the environment. Accordingly, there has been an international movement toward restricting the use of lead. For this reason, non-lead-containing (that is, lead-free) ferroelectric materials, unlike PZT, have been in demand.
One of the lead-free ferroelectric materials that are currently under development is, for example, a perovskite-type composite oxide [(Bi0.5Na0.5)1-yBay]TiO3 made of bismuth (Bi), sodium (Na), barium (Ba), and titanium (Ti). Patent Literature 1 and Non Patent Literature 1 disclose that this ferroelectric material exhibits high piezoelectric performance of about 125 pC/N in terms of a piezoelectric constant d33, when the [(Bi0.5Na0.5)1-yBay]TiO3 has composition around the Morphotropic Phase Boundary with the content of barium y (=[Ba/(Bi+Na+Ba)]) is 5 to 10%. The piezoelectric performance of the ferroelectric material is, however, lower than that of PZT.
Patent Literature 2, Non Patent Literature 2, and Non Patent Literature 3 disclose that a (Bi,Na,Ba)TiO3 layer that is oriented in a specific direction is fabricated.
The non-obviousness from Patent Literature 3 in view of Patent Literature 4 is described later.